Multi-processor platform for wireless communication terminal having partitioned protocol stack

ABSTRACT

A multi-mode wireless communication device and multi-mode communication method are disclosed. The multi-mode device includes a first baseband co-processor configured to execute low-level stack operations of a first wireless communications protocol employed within a first wireless communications network. The device also includes a host baseband processor configured to execute a set of protocol stack operations of a second wireless communications protocol employed within a first wireless communications network and higher-level stack operations of the first wireless communications protocol. A data communication channel capable of carrying data received by the multi-mode wireless communication device from the first wireless communications network or sent by the multi-mode wireless communication device through the first wireless communications network is provided between at least the host baseband processor and the first baseband co-processor.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority under 35 U.S.C. §119(e) tocopending U.S. Provisional Patent Application Serial No. 60/434,448,entitled MULTI-PROCESSOR PLATFORM FOR WIRELESS COMMUNICATION TERMINALHAVING PARTITIONED PROTOCOL STACK, and is related to copending U.S.patent application Ser. No. ______, filed Dec. 11, 2003, and entitledSYNCHRONIZATION OF MULTIPLE PROCESSORS IN A MULTI-MODE WIRELESSCOMMUNICATION DEVICE.

FIELD OF THE INVENTION

[0002] The present invention relates to wireless communication systemsand, more particularly, to a multi-processor platform for a wirelesscommunication terminal having a partitioned protocol stack.

BACKGROUND OF THE INVENTION

[0003] It is becoming increasingly apparent that communication systemsinvolving fixed client terminals and server units are no longer the onlypervasive means of communication available to large segments of society.In particular, certain current and next-generation client devices are nolonger tied to use at a single physical location or limited to a singleapplication. Such portable client terminals are predicted to emerge asubiquitous communication and computing platforms, capable of enablingthe convergence of consumer electronics, computing, and communications.In order for this type of convergence to fulfill its promise, clientterminals will need to become capable of accessing a multiplicity ofapplications and services while seamlessly connecting to a variety ofwireless access networks.

[0004] Such convergence may be evaluated from at least two perspectives.First, the manner in which multiple wireless networks may be configuredto facilitate such convergence needs to be considered. This will enablethe creation of user scenarios aiding in the development of mobileterminal architectures designed to interoperate with such multiplenetworks. Secondly, convergence from the perspective of end-users shouldbe understood in order that any proposed system solutions accommodatethe needs of such end-users to the greatest extent possible givenapplicable network constraints.

[0005] From a network perspective, efforts are being made to achievesuch convergence through integration of wireless local area networks(“WLANs”) and third-generation (“3G”) cellular systems developed inaccordance with the Universal Mobile Telecommunications System (UMTS).Such 3G cellular systems include, for example, integrated systems basedupon Global System Mobile (GSM) and General Packet Radio Service (GPRS)(i.e., GSM/GPRS systems), as well as wideband code division multipleaccess systems (WCDMA). Varying degrees of integration of a 3G cellularsystem and a WLAN may be achieved. For example, a certain degree ofintegration may be obtained merely through sharing of billing andsubscriber profile information. On the other hand, a relatively greaterdegree of integration may be achieved through integration of the corenetwork functionality of the WLAN and the 3G cellular system. Althoughthe latter approach promises to yield a more complete set of networkfunctions, it would constitute an extremely complicated and expensiveundertaking. Furthermore, in view of the evolving nature of both theWLAN and UMTS standards, near term prospects of comprehensiveintegration of WLAN and 3G cellular systems seem rather dim.Accordingly, it is probable that the former type of integration andcoordination among systems will likely be the only approach to beimplemented within the foreseeable future.

[0006] Turning now to FIG. 1, an illustrative representation is providedof an exemplary wireless communication system 100 within which theformer type of integration may be attained by connecting the billing andsubscriber profiles for a WLAN 104 and a UMTS network 106. As may beappreciated from FIG. 1, the WLAN 104 and UMTS network 106 share acommon authentication system 110 and a common billing system 114.

[0007] The UMTS network 106 is comprised of several primary portionsincluding a mobile subscriber terminal 118 and associated SubscriberIdentity Module (SIM) 120, a UMTS radio network 124, and a UMTS corenetwork 126 containing switching infrastructure and networkintelligence. During operation of the system 100, the subscriberterminal 118 communicates with base stations within the UMTS radionetwork 124. Such base stations convert radio signals from thesubscriber terminal 118 into digital signals which are provided to theswitching infrastructure within the UMTS core network 126. Thisswitching infrastructure establishes call connections with othersubscriber terminals, or routes the digital signal information to thepublic switched telephone network (PSTN) or other data network (e.g.,the public packet data network (PPDN) or the Internet).

[0008] The SIM 120 is realized as an electronic card and providessubscriber identity information to the subscriber terminal 118, whichtransmits this information to the UMTS radio network 124 in order togain access to the UMTS core network 126. The UMTS core network 126 thenverifies the validity of the subscriber identification informationbefore authorizing access to the subscriber terminal 118. Within theUMTS network 106, the SIM 120 is used as the primary subscriberidentification and encryption mechanism, although this capability hasnot been standardized within WLAN environments. However, severalapproaches have been proposed for development of authentication andencryption solutions for deployment within WLANs using SIM/USIMtechnology.

[0009] It is anticipated that SIM/USIM technology will play a key rolein enabling the convergence of WLAN and cellular systems at a networklevel by enabling joint authentication (and by implication alsobilling). It is further believed that this technology may play a keyrole in solving many of the security issues that have hindereddeployment of WLAN systems.

[0010] From an end-user perspective, the promise of third generationwireless systems has always been the delivery of a diverse range ofservices to anyone, anywhere, anytime and at the lowest possible cost.During the early stages of the development of UMTS networks, the visionwas that the combination of existing GSM/GPRS networks with the newlydeveloped WCDMA networks would fulfill this promise. However, thedevelopment and commercialization of WLAN technologies (specifically802.11a/b) has been gaining momentum. Among many experts, the currentconsensus seems to be that both systems will co-exist. In this regard itappears that end users will be less concerned with the availability of aparticular technology than with the reliable delivery of multipledifferent types of advanced services. In order to enable suchconvergence of service offerings, network operators must ensure theavailability of subscriber terminals capable of securely executing anumber of different applications. In addition, it will also be desiredto deliver such advanced services using the lowest-cost networkinfrastructure available. Accordingly, the architecture ofnext-generation mobile terminals will ideally be capable of receivingservices or applications via a number of different bearer options (e.g.GSM/GPRS, WCDMA, and 802.11a/b).

[0011] Turning now to FIG. 2, a block diagram is provided of thebaseband platform of a typical second generation (2G) wireless handset200. As shown, handset 200 typically includes a processor 204 (e.g., anARM7 or the equivalent) and a 16-bit DSP 208. Firmware of the DSP 208 istypically executed from ROM (not shown), while software executed by theprocessor 204 is stored in “off-chip” FLASH memory 212. The handset 200also typically includes a limited amount of off-chip SRAM 216, as wellas a SIM interface 220 configured to accept an electronic SIM card ofthe type described above. With slight modification, the platform 200 mayalso be used to implement dual-mode GSM/GPRS solutions. Typically, aprocessor 204 of higher speed (e.g., an ARM9 processor) is used in theGSM/GPRS handset, and the clock speed of the 16-bit DSP 208 is alsoincreased. A higher-speed processor 204 such as the ARM9 is not onlycapable of running the GSM/GPRS protocol stack, but also of concurrentlyexecuting applications.

[0012] Accordingly, from an end user perspective a number of theingredients necessary to support convergence are present within existinghandset technology; namely, sufficient processing and computingcapability to underpin a number of different applications and services,and a SIM interface enabling subscriber access to a unifiedauthentication and billing platform. However, existing handsets aregenerally incapable of supporting multiple radio protocols or “bearers”,thereby limiting the convergence of the different services offered viavarious bearers. For example, certain existing GSM handsets are capableof accessing and displaying information via Internet web browsing, butare not disposed to seamlessly roam between GSM networks and other typesof radio networks such as, for example, WLAN, Bluetooth or 3G WCDMAnetworks.

[0013] Accordingly, it would be desirable to provide for seamlessmobility between radio networks operative in accordance with differentprotocols. In order enable such mobility and the consequent convergencein services, it would also be desirable to provide a mobile wirelessterminal that inexpensively supports multiple bearers and services, andthat further enables service differentiation based upon user identity.

SUMMARY OF THE INVENTION

[0014] In summary, the present invention relates in one aspect to amulti-mode wireless communication device including a first basebandco-processor configured to execute low-level stack operations of a firstwireless communications protocol employed within a first wirelesscommunications network. The wireless device also includes a hostbaseband processor configured to execute (i) a set of protocol stackoperations of a second wireless communications protocol employed withina first wireless communications network, and (ii) higher-level stackoperations of the first wireless communications protocol. A datacommunication channel is provided between the host baseband processorand the first baseband co-processor and is capable of carrying datareceived by the multi-mode wireless communication device from the firstwireless communications network or sent by the multi-mode wirelesscommunication device through the first wireless communications network.In a particular implementation the set of protocol stack operationsexecuted by the host baseband processor comprises a complete set ofprotocol stack operations of the second wireless communicationsprotocol. In other implementations the wireless device further includesa second baseband processor configured to execute low-level stackoperations of the second wireless communications protocol, withhigher-level protocol stack operations of the second wirelesscommunications protocol being executed by the host baseband processor.

[0015] The present invention also relates to a method performed in awireless communication device disposed for communication with first andsecond wireless communications networks in accordance with first andsecond wireless communication protocols, respectively. The methodincludes executing low-level stack operations of the first wirelesscommunications protocol within a first baseband co-processor. A set ofprotocol stack operations of a second wireless communications protocoland higher-level stack operations of the first wireless communicationsprotocol are also executed within a host baseband processor. A datacommunication channel capable of carrying data received by the wirelesscommunication device from the first wireless communications network orsent by the wireless communication device through the first wirelesscommunications network is established between the host basebandprocessor and the first baseband co-processor. In a particularimplementation the method further includes executing low-level stackoperations of the second wireless communications protocol within asecond baseband processor in communication with the host basebandprocessor via the data communication channel.

[0016] In another aspect the invention is directed to a multi-modewireless communication device including a first bearer-specificprocessor configured to execute low-level stack operations of a firstwireless communications protocol employed within a first wirelesscommunications network. The device also includes a secondbearer-specific processor configured to execute low-level stackoperations of a second wireless communications protocol employed withina second wireless communications network. A primary processor configuredto execute higher-level stack operations common to the first and secondwireless communications protocols is also provided. The deviceadditionally includes a radio transceiver, and an arrangement forcommunicating data between the radio transceiver, the primary processor,the first bearer-specific processor and the second bearer-specificprocessor. In a particular implementation the low-level stack operationsof the first wireless communications protocol include physical layerfunctions and bearer-specific stack functions peculiar to the firstwireless communications protocol. Similarly, the low-level stackoperations of the second wireless communications protocol may includephysical layer functions and bearer-specific stack functions peculiar tothe second wireless communications protocol.

[0017] The present invention also pertains to a multi-mode wirelesscommunication device including a first integrated circuit configured toexecute low-level stack operations of a first wireless communicationsprotocol employed within a first wireless communications network. Thedevice also includes a second integrated circuit configured to executelow-level stack operations of a second wireless communications protocolemployed within a second wireless communications network. Also includedwithin the device is a third integrated circuit configured to executehigher-level stack operations of the first wireless communicationsprotocol and of the second wireless communications protocol. A firstdata communications channel is provided between the first integratedcircuit and the third integrated circuit, and a second datacommunications channel is provided between the second integrated circuitand the third integrated circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] For a better understanding of the nature of the features of theinvention, reference should be made to the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

[0019]FIG. 1 provides an illustrative representation of an exemplarywireless communication system in which the billing and subscriberprofiles for a wireless LAN and a UMTS network are connected.

[0020]FIG. 2 is a block diagram of the baseband platform of a typicalsecond generation (2G) wireless handset.

[0021]FIG. 3 illustratively represents an exemplary layered softwarearchitecture of the present invention disposed within a mobile wirelesscommunication terminal.

[0022]FIG. 4 is a block diagrammatic representation of a mobile terminalincorporating a layered software architecture partitioned among multipleprocessors in accordance with the invention.

[0023]FIG. 5 provides a more detailed illustrative representation of amulti-strata software architecture as configured for incorporationwithin a multi-bearer wireless terminal.

[0024]FIG. 6 illustratively represents a wireless terminal basebandplatform obtained through mapping of the multi-strata softwarearchitecture of FIG. 5 to an existing GSM/GPRS platform architecture.

[0025]FIG. 7 illustrates a dual-mode wireless terminal baseband platformconfigured to provide both GSM/GPRS and WCDMA bearer services.

[0026]FIG. 8 illustrates a dual-mode wireless terminal baseband platformwhich illustrates the convergence of multiple user applications into asingle device.

[0027]FIG. 9 shows a tri-mode wireless terminal platform configured toprovide both GSM/GPRS, WCDMA and wireless local area network (WLAN)bearer services in accordance with the invention.

[0028]FIG. 10 depicts a block diagram of an exemplary embodiment of aconvergent multi-mode wireless terminal platform of the presentinvention.

[0029]FIG. 11 illustrates a dual-mode wireless terminal basebandplatform with respect to which will be described the provision of bothGSM/GPRS and WCDMA bearer services in a time-synchronized manner.

[0030]FIG. 12 provides an illustrative representation of a countermaintained by a WCDMA master timer of a WCDMA baseband co-processor.

[0031]FIG. 13 shows a timing diagram which illustratively represents atiming synchronization method predicated upon execution of a directaccess read operation.

[0032]FIG. 14 depicts a timing diagram illustratively representing atiming synchronization method predicated upon execution of an interruptcapture operation.

DETAILED DESCRIPTION OF THE INVENTION

[0033]FIG. 3 illustratively represents an exemplary layered softwarearchitecture 300 of the present invention as configured for inclusionwithin a mobile wireless communication terminal 310. The layeredsoftware architecture 300 includes an application layer 314 incommunication with a common stack functions layer 316. As is indicatedby FIG. 3, a set of software routines defining an overall communicationprotocol for the mobile wireless communication terminal 310 are groupedinto a stack of protocol layers; i.e., a protocol stack, comprised ofthe common stack functions layer 316, a bearer-specific stack layer 320and a physical layer 324. The protocol stack divides the overallcommunication protocol into hierarchical layers of functionality.

[0034] As may be appreciated with reference to FIG. 3, the “lower”protocol layers comprised of the bearer-specific stack layer 320 andphysical layer 324 are specific to a particular communication protocoland radio transceiver design, respectively. In contrast, the “upper”protocol layers comprised of the application layer 314 and common stackfunctions layer 316 are substantially independent of a particularcommunications protocol and transceiver design. It follows that incertain implementations it will be convenient to bifurcate theprocessing of such upper and lower protocol layers among first andsecond processor modules 330 and 334, respectively. In this way anysecond processor module 334 configured to implement a desired radiobearer and transceiver functionality may be inserted within the terminal310 and communicate with the higher layer protocols executed by thefirst processor module 330.

[0035] It is thus apparent that the functionality of the layeredsoftware architecture 300 may be distributed as desired among aplurality of physical processing modules used to realize thecommunication terminal 310. Advantageously, the common stack functionslayer 316 permits the data streams received from the bearer-specificstack layer 320 to appear the same to the application layer 314irrespective of the particular communications protocols beingimplemented by such stack layer 320. This distribution of functionalityenables such additional processing modules 334 to be removed andreplaced with other modules configured to implement differentcommunication protocols.

[0036] Referring to FIG. 3, the application layer 314 is comprised of anumber of distinct application programs 342 (e.g., voice communication,web browsing, streaming video). Each application program 342 interactswith the common stack functions layer 316, which provides access to aparticular bearer communication channel (e.g. GSM/GPRS, 802.11 orWCDMA). For example, in the case of WCDMA the common stack functionslayer 316 would implement the functionality of the Non-Access Stratum(NAS), which performs user authentication based upon the informationincluded within the SIM card 350 inserted into the mobile terminal 310.Since the NAS is executed by the first processing unit 330 independentof any bearer-specific processing unit 334, this authentication processis advantageously effected in a bearer-independent manner. That is, inthis embodiment the user will always be authenticated using theinformation within the SIM card 350 irrespective of whether the chosenbearer is WCDMA, 802.11 or GSM/GPRS.

[0037] Turning now to FIG. 4, a block diagrammatic representation isprovided of a mobile terminal 400 incorporating a layered softwarearchitecture partitioned among multiple processors in accordance withthe present invention. As shown, the mobile terminal 400 includes afirst processor 410 disposed to execute application layer routines and aset of common stack functions as described above with reference to FIG.3. The mobile terminal 400 further includes a plurality ofbearer-specific processors 414, each of which is configured to implementthe bearer-specific and physical layers of the protocol stack for agiven radio bearer. A conventional keyboard module 418 is interactivelycoupled to the processor 410, which may be implemented as a 16-bitmicroprocessor having ROM, RAM, a plurality of ports, analog to digitalconverters and a serial interface. In addition to the on-chip memorycapacity, an external ROM 420 and an external RAM 424 may be providedfor additional data processing and communication capacity. The terminal400 further includes a display controller and associated driver circuits430 configured to drive an LCD screen 434.

[0038] As is described hereinafter, in a particular embodiment theinventive software architecture 300 enables new radio bearers to beadded to an existing GSM/GPRS platform (see, e.g., FIG. 2) withoutmodification of the processing modules effecting the core GSM/GPRSfunctionality. In this way the present invention enables the re-use ofexisting GSM/GPRS solutions, thereby permitting development of mobileterminal platforms facilitating convergence from both network and userperspectives. As a result, wireless semiconductor and mobile devicemanufacturers may efficiently and cost effectively migrate theirexisting single-mode GSM/GPRS platforms to dual-mode (GSM/GPRS & WCDMA)or even multi-mode (GSM/GPRS, WCDMA & 802.11) solutions. This enablesthe efficient and economical addition of new bearers with minimalredesign of existing mobile terminal platforms.

[0039] Turning now to FIG. 5, a more detailed illustrativerepresentation is provided of the software architecture 500 of thepresent invention as configured for incorporation within a multi-bearerwireless terminal. As shown, the architecture 500 is organized within aset of four software strata, each of which is defined by different dataflow characteristics: an application stratum 504, communication stratum506, protocol stratum 508 and a physical stratum 510.

[0040] In the exemplary embodiment the application stratum 504 iscomprised of a plurality of user-level application programs 520 (e.g.,web browsing, text messaging). As a consequence, the data transfersoccurring across the interface 524 between the communication stratum 506and the application stratum 504 will tend to be “bursty” in nature.

[0041] The communication stratum 506 implements bearer-independentprotocol stack functionality pertinent to maintenance of calls or otherconnections. In this regard the communication stratum 506 functions toauthenticate users on various networks, select an appropriate bearer touse in transport of data packets, and maintain connections at theapplication level while switching between such bearers. That is, thecommunication stratum 506 provides application programs 520 access todifferent bearers, and provides authentication service for all bearersusing SIM/USIM mechanisms. The data rates across the interface 530between the communication stratum 506 and the protocol stratum 508 willtend to be more consistent than across the interface 524.

[0042] The protocol stratum 508 implements various bearer-specificprotocol stack functions 534, and is configured to accommodaterelatively high peak data rates across the interface 536 with thephysical stratum 510. As shown, the physical stratum 510 is comprised ofa number of physical layer modules 550 corresponding to various bearers(e.g., GSM/GPRS, WCDMA and 802.11). It should be noted that FIG. 5provides a hierarchical view of the software architecture of FIG. 5,which is not constrained to be mapped to a particular hardwareconfiguration.

[0043] As may be appreciated from FIG. 5, the multi-strata softwarearchitecture 500 relies upon buffering in order to equalize the dataflow among the four defined software strata. Specifically, theapplication stratum 504 includes a plurality of buffers 556 respectivelyassociated with the plurality of application programs 520, the protocolstratum includes a plurality of buffers 560 respectively associated witheach bearer-specific stack functions 534, and the physical stratum 510includes a plurality of buffers 564 respectively associated with eachphysical layer module 550. As is described hereinafter, the buffers 556,560 and 564 enables the software architecture 500 to be implementedusing a number of different hardware configurations.

[0044] As an initial example, FIG. 6 illustratively represents awireless terminal baseband platform 600 obtained through mapping of theinventive multi-strata software architecture 500 to an existing GSM/GPRSplatform architecture. The platform 600 is realized using a singlebaseband integrated circuit or “chip” 601 comprised of a processor 604(e.g., an ARM9 processor) and a digital signal processor (DSP) 608. Inthis approach, the functions associated with the communication stratum508, protocol stratum 506 and SIM/USIM authentication process 602 areexecuted by the processor 604. As shown, the processor 604 executescommon stack functions 620, as well as bearer-specific GSM stackfunctions 622 and GPRS stack functions 624. Buffers 630 and 632 serve toaccommodate the different data rates associated with execution of thecommon stack functions 620 and the bearer-specific GSM and GPRS stackfunctions 622 and 624. Typically, data to be transmitted over the air isstored in on-chip SRAM 616 in order to enable efficient access to suchdata in connection with the addition or removal of header informationand the like.

[0045] As is indicated by FIG. 6, the physical stratum 510 isimplemented using the DSP 608. Although the GPRS physical layer module650 ₂ will typically re-use the functionality of the GSM physical layermodule 650 ₁, from a logical perspective distinct GSM and GPRSfunctionality may be split among the modules 650 ₁ and 650 ₂ asindicated. As shown, the interface between the protocol stratum and thephysical stratum is implemented as an on-chip mailbox 610 containing afirst physical stratum buffer 660 ₁ associated with the GSM physicallayer module 650 ₁ and a second physical stratum buffer 660 ₂ associatedwith the GPRS physical layer module 650 ₂.

[0046] Turning now to FIG. 7, there is illustrated a dual-mode wirelessterminal baseband platform 700 configured to provide both GSM/GPRS andWCDMA bearer services. As shown, the baseband platform 700 isarchitected similarly to the platform 600, and includes a GSM/GPRS hostbaseband processor platform 701 comprised of a processor 718 (e.g., anARM9 processor) and a digital signal processor (DSP) 708. However, theplatform 700 further includes a WCDMA baseband co-processor 704containing a WCDMA physical layer module 708 and associated buffer 710.The WCDMA baseband co-processor 704 operates to perform physical layerprocessing of WCDMA bearer signals, and interfaces with abearer-specific WCDMA stack functions 716 executed by the host processor718. A buffer 722 accommodates the generally different data transferrates associated with execution of the common stack functions 720 andthe WCDMA stack functions 716.

[0047] In the embodiment of FIG. 7, the WCDMA stack functions 716implemented using the processor 916 include the bearer-specificfunctions MAC, RLC, PDCP, BMC and RRC. In like manner the processor 916is used to implement the common stack functions 720, which inWCDMA-based configurations would include NAS functions. Finally, theWCDMA baseband co-processor 704 is responsible for all WCDMA-related“Layer 1” or physical layer functions.

[0048] Again referring to FIG. 7, prudent engineering design suggeststhat the additional processing burden placed upon the processor 718 as aconsequence of the addition of a WCDMA bearer should be evaluated. As aninitial matter, the processing overhead associated with execution of thebearer-specific WCDMA stack module 716 is considered. For example,assuming that the WCDMA stack function 716, GSM stack functions 622, andGPRS stack functions 624 collectively require 30 MIPS of processingpower, the processing activity of the processor 718 is profiled below inTable I. TABLE I MIPS available (@ 104 MHz) 104 Number of wait statesfor  10 external memory access Cache hit ratio 83% Stack MIPSrequirement  30 MIPS Remaining 104 − 30 * 0.83 − (30 * 0.17 * 10) = 28.1

[0049] As may be apparent from Table I, the processor 718 possessessufficient processing resources to implement both the bearer-specificWCDMA stack function 716 and GSM/GPRS stack functions 622 and 624. Thatis, the present invention enables the mapping of the WCDMA stackfunction 716 onto a processor of the type employed in realizing existingGSM/GPRS solutions, while providing a WCDMA baseband co-processor 704 toeffect the WCDMA physical layer functions. Since the WCDMA physicallayer is anticipated to be of substantially greater complexity than theGSM/GPRS physical layers, it may often be appropriate to realize theWCDMA baseband co-processor 704 as an application specific integratedcircuit (ASIC) rather than using a general purpose digital signalprocessor (DSP). It is also of course possible to integrate all of therequired physical, protocol and communications stratum GSM/GPRS andWCDMA functionality within a single baseband integrated circuit, butthis nullifies the advantages associated with the modular approachdescribed above.

[0050] As indicated above, when a pair of integrated circuits (i.e.,host baseband processor platform 701 and WCDMA baseband co-processor704) are used to implement the dual-mode platform 700, memory mapping isused to define the interface between the protocol stratum and thephysical stratum. Since this interface has the benefit of beingstandardized, the augmentation of existing 2.5 G platforms to includeWCDMA functionality in accordance with the invention is simplified. Thememory mapping defining this interface will typically be effected byestablishing a shared area within the memory of the host basebandprocessor platform 701. This shared memory space may be logicallyconfigured as a dual-port RAM segmented into a number of areas, eachcontaining a different type of data. These data types may comprise, forexample, control information transferred between the protocol stacks andphysical layers and uplink/downlink data. During operation of theplatform 700, this shared memory space facilitates the exchange of databetween the host baseband processor platform 701 and WCDMA basebandco-processor 704 at regular intervals. Typically, such an interval willcorrespond to the duration of a frame (e.g., 10 ms in the case ofWCDMA). At the end of each frame, the WCDMA baseband co-processor 704will interrupt the host baseband processor platform 701 and signal thatnew information is available for reading. When the host basebandprocessor platform 701 reads such new information, it also writes newinformation into the shared memory space for reading by the WCDMAbaseband co-processor 704. In the exemplary embodiment the host basebandprocessor platform 701 may interrupt the WCDMA baseband processor 704 atany time should it desire to write new data into the shared memoryspace.

[0051]FIG. 8 illustrates a dual-mode wireless terminal baseband platform800 which illustrates the manner in which the present inventionfacilitates convergence of user applications into a single device. Aswas demonstrated above with reference to Table I, the present inventionenables existing 2.5 G platforms to be augmented to accommodate newhigh-speed bearer services (e.g., WCDMA) while retaining sufficientsignificant processing resources to permit execution of userapplications. For example, if the subject device is a feature phone, theremaining processing resources could be used to execute an applicationenabling decoding of a multi-media message or the like. Should moreadvanced application execution capabilities be required, thearchitecture depicted in FIG. 8 may be employed. As shown, in theembodiment of FIG. 8 the application stratum 504 has been mapped to anapplication processor 804 external to the host baseband processorplatform 701. The application processor 804 is configured to run anoperating system capable of executing complex applications such as, forexample, MPEG-4 encoding or the equivalent. As is illustrated by FIG. 8,the application processor 804 may be connected to the host basebandprocessor platform 701 using a relatively fast serial connection 810. Ingeneral, the buffering of data between the application stratum 504 andthe communication stratum 506 may be handled by the applicationprocessor 804.

[0052] Referring now to FIG. 9, there is shown a tri-mode wirelessterminal platform 900 configured to provide both GSM/GPRS, WCDMA andwireless local area network (WLAN) bearer services. As a consequence ofthe high peak data rates characterizing various WLAN protocols (e.g.,IEEE 802.11), in the embodiment of FIG. 9 the protocol stratum 508 isseen to be implemented across a host baseband processor platform 901 anda WLAN baseband co-processor 904. As shown, the protocol stratum 508 forthe WLAN bearer is comprised of a WLAN upper medium access control (MAC)layer 908 executed by a processor 916, and a WLAN lower MAC & physicallayer 910 executed by the WLAN baseband co-processor 904. The WLAN upperMAC layer 908 will generally be executed by the host baseband processorplatform 901. This bifurcation of the processing of the WLAN MAC layerwill generally be desirable in view of the lower processing requirementsassociated with execution of the WLAN upper MAC layer 908 relative toexecution of the WLAN lower MAC & physical layer 910; that is, executionof the WLAN lower MAC & physical layer 910 requires relatively moreprocessing power and such execution will thus often be effected using aseparate chip. Again, the different data flow characteristics of theWLAN upper MAC layer 908 and the WLAN lower MAC & physical layer 910 areaccommodated using buffers 920 and 924, respectively.

[0053] When considering the addition of a new bearer to the inventivewireless terminal platform, at least two parameters will generallywarrant consideration; namely, the peak and average data rates. Whilethe peak data rate of the new bearer may be relatively high, averagedata rates may be significantly lower. For example, in the case of both802.11b and WCDMA bearers the average data rates will typically be inthe range of approximately only 200-384 kbps, while peak data rates maybe significantly higher. This phenomenon tends to arise for at least tworeasons. First, the 11 Mbps communication bandwidth offered by 802.11bsystems is shared by all users within the applicable coverage area or“hotspot”. Secondly, data and video compression enable betterutilization of bandwidth and thus require a lower average data rate. Inaccordance with the invention, splitting of the MAC layer in the mannerdescribed above may prevent bottlenecks from developing across thememory interfaces associated with the host baseband processor platformduring the processing of such peak data rates. By such splitting of theMAC layer, the peak data rate associated with processing of the lowerMAC portions by a separate WLAN baseband chip may be on the order of 11Mbps, while the average data rate associated with processing of theupper MAC portions via the host baseband processor platform may be muchlower (e.g., 300-400 Kbps).

[0054] From a logical perspective, each physical stratum buffer (i.e.,the buffers 660, 710 and 924) is implemented as a dual-port RAM in theembodiment of FIG. 9. In the case of the physical stratum buffer 710, afirst port is read and written to by the host baseband processorplatform 901 while a second port of the buffer 710 is asynchronouslyaccessed by the WCDMA physical layer 708. It will generally be preferredto implement the buffer 710 such that the WCDMA baseband co-processor704 does not serve as a master on the bus connected thereto. Thisresults in all accesses of the first port being initiated by the hostbaseband processor platform 901, which permits the bus to be easilyshared by program and data memory.

[0055] Each protocol stratum buffer (i.e., the buffers 630, 632, 722 and920) generally constitutes a block of locations within the memory of thehost baseband processor platform 901. This memory space may be allocatedstatically or dynamically, and is used primarily as a repository fordata to be potentially re-transmitted to the extent required by theapplicable Layer 2 protocols. For example, in the case of TCP theprotocol stratum 508 may transmit a packet out and then wait for anacknowledgement (i.e., an ACK) to be received from the TCP peer to whichthe packet was transmitted. If an ACK is not received, the subject datais retransmitted from the protocol stratum 508. In this case thecommunication stratum 506 is not involved in the retransmission, whichis consistent with an architecture in which such retransmission isimplemented as a bearer specific function.

[0056] Similar to the protocol stratum buffers, an application stratumbuffer (not shown) generally constitutes a block of locations within thememory of the host baseband processor platform 901. This bufferfunctions to store data generated by applications until such data isready for transmission. In this way the application stratum buffersupports the switching of the communication stratum between bearers ofdifferent speeds.

[0057] Referring again to FIGS. 7-9, the common stack functions 720generally comprise various stack functions applicable to the bearerssupported by the platform 700. One such common stack function 720 whichwill generally be implemented is the Session Management function. As anexample of such implementation, consider the case when the wirelessterminal platform of the present invention is incorporated within awireless terminal used to browse the Web. In this case the wirelessterminal would initiate a TCP/IP session, during which the IP packetscould be transported via any supported bearer (e.g. WCDMA or 802.11).That is, when a user of the wireless terminal “opens” its browserprogram, a connection (CI) is created through which a particular bearer(e.g., WCDMA) is used to transport the IP packets. Assume next that theuser enters a hotspot area in which a faster 802.11 air interface isavailable. This situation is detected by the communication stratum 506,which will now invoke the 802.11 air interface to carry the IP packets.However, the connection is still C1 from a session perspective, and theuser of the wireless terminal will be unaware that a different physicallayer is being used to actually transport the IP packets.

[0058] The common stack functions 720 may also implement variousauthentication operations. To this end the common stack functions 720will often contain all the software necessary to, for example, read aSIM card and generate the secure keys and the like necessary to encryptdata in connection with a desired authentication operation.

[0059] Again directing attention to FIGS. 7-9, in the exemplaryembodiment the bearer-specific WCDMA stack functions 716 are comprisedof the following: MAC (Medium Access Control), RLC (Radio Link Control),PDCP (Packet Data Converge Protocol) and RRC (Radio Resource Control).The MAC, RLC and PDCP functions are involved in regulating functionalitywithin the data domain, while the RRC is responsible for controlfunctionality. In contrast, bearer-specific WLAN protocol stacksgenerally consist only of a MAC layer. In both cases, at least threeprimary constraints applicable to the bearer specific protocol stackfunctions should be considered in determining the manner in which theterminal architecture of the present invention may be configured tosupport convergence. Specifically, these constraints relate to the codespace, data space and MIPS required to integrate multiple bearers usingthe approaches described above.

[0060] Required Code Space

[0061] The total code space required to implement a GSM/GPRS stack willbe somewhat dependent upon the details of various implementations, butis generally expected to require an average of approximately 1.1 MB ofprogram memory. As is indicated by Table II, moving to a dual-modeGSM/GPRS & WCDMA solution will tend to increase this code spacerequirement to approximately 3 MB. However, the addition of an 802.11bbearer is expected to have only negligible impact upon program memoryrequirements. This is because the complexity of the WCDMA protocol stackis such that its size will typically be largely determinant of overallprogram memory requirements. TABLE II Technology Code Space RequiredGSM/GPRS 1.1 MBytes WCDMA 1.9 MBytes

[0062] Required Data Space

[0063] As in the case of code space requirements, overall data spacerequirements will be dependent upon the specifics of variousimplementation approaches. However, it is generally anticipated that asingle mode GSM/GPRS solution will require approximately 512 KB of datamemory. As is indicated by Table III, extending this solution to adual-mode GSM/GPRS & WCDMA implementation will tend to increase thememory requirements to 1 MB. Similarly, the addition of an 802.11bbearer will generally require an additional 128 KB of data memory. TABLEIII Technology Data Space Required GSM/GPRS 512 KBytes WCDMA 512 KBytesWLAN 128 KBytes

[0064] MIPS Required

[0065] The third parameter which should be considered in the design ofthe converged terminal architecture of the present invention relates tothe processing resources required by the various bearer services whichmay be supported. In the specific cases of WCDMA and 802.11, differentfactors will be determinative of the required processing resources. Inthe case of 802.11a/b, the primary factor is the maximum data ratesupported. In contrast, the required control overhead associated with aWCDMA bearer will typically primarily account for its consumption ofprocessing resources. As indicated by Table IV, it is expected thatexecution of an exemplary implementation of an 802.11a/b WLAN MAC willrequire approximately 10 MIPS (assuming zero wait state access to allmemories), while execution of a WCDMA service at 384 kbps will requireapproximately 30 MIPS. TABLE IV Technology MIPS Required GSM/GPRS <10MIPS   WCDMA 30 MIPS WLAN 10 MIPS

[0066] Attention is now directed to FIG. 10, which depicts a blockdiagram of a particular physical implementation of a multi-mode wirelessterminal platform 1000 consistent with the present invention. Themulti-mode terminal platform 1000 is configured for implementationwithin a wireless terminal (not shown) possessing GSM/GPRS, WCDMA and802.11a/802.11b bearer capabilities. The inventive platform 1000 isimplemented using a three distinct integrated circuits; however, theWCDMA and WLAN functionalities could easily be integrated into a singlechip if desired. As shown in FIG. 10, the platform 1000 includes aGSM/GPRS chip 1002 as modified to implement WCDMA and 802.11 upper levelMAC protocol stack functionality in the manner described above. TheGSM/GPRS chip 1002 is connected to a WCDMA chip 1004 operative to effectphysical layer processing of the WCDMA bearer. Similarly, the GSM/GPRSchip 1002 is connected to a 802.11 chip 1010 configured to execute thelower MAC & physical layers of an 802.11 bearer. As shown, the GSM/GPRSchip 1002 also interfaces with SRAM 1014 and flash memory 1020. Theplatform 1000 advantageously affords a significant degree of flexibilityas various types of terminals may be developed using a common set ofchip designs. In this way a given GSM/GPRS chip design may be used toproduce wireless terminals having at least the following types ofcapabilities: single-mode GSM/GPRS; dual-mode GSM/GPRS & WCDMA;dual-mode GSM/GPRS & 802.11; and multi mode GSM/GPRS, WCDMA & 802.11.

[0067] In a particular implementation of the wireless terminal platform1000, the WCDMA chip 1004 may be realized using, for example, aSPINNERcore chip available from Zyray Wireless of San Diego, Calif.Similarly, the 802.11 chip 1010 may be implemented using an HFA 3860 oran HFA 3724 from Intersil Corporation of Irvine, Calif.

[0068] Turning now to FIG. 11, there is illustrated a dual-mode wirelessterminal baseband platform 1100 with respect to which will be describedthe provision of both GSM/GPRS and WCDMA bearer services in atime-synchronized manner. As shown, the baseband platform 1100 includesa “host” GSM/GPRS baseband processor 1101 comprised of a Layer 2processor 1108 and a GSM/GPRS modem 1110. In the exemplary embodimentthe Layer 2 processor 1108 comprises an ARM9 processor available fromARM, Inc. As shown, the host baseband processor 1101 further includes amaster timer 1112 adapted to maintain counter values utilized by theGSM/GPRS modem 1110. The platform 1100 further includes a WCDMA basebandco-processor 1104, which contains a WCDMA modem 1116. The WCDMA basebandco-processor 1104 further includes a master timer 1118 configured tomaintain counter values utilized by the WCDMA modem 1116. The WCDMAbaseband co-processor 1104 operates to perform physical layer processingof WCDMA bearer signals, and interfaces with the host baseband processor1101 through a baseband interface 1122. Various bearer-specific WCDMAstack functions are executed by the Layer 2 processor 1108 with respectto WCDMA bearer signals communicated to and from the WCDMA modem 1116via the baseband interface 1122. In the embodiment of FIG. 11, thebaseband interface 1122 comprises a shared area within the memory of theWCDMA baseband co-processor 1104. This shared memory space may belogically configured as a dual-port RAM segmented into a number ofareas, each containing a different type of data. These data types maycomprise, for example, control information transferred between theprotocol stacks and physical layers and uplink/downlink data. As shown,communication between the baseband interface 1122 and the WCDMA mastertimer 1118 may be effected via a direct access read operation 1150 orover an Advanced High Speed (AHB) bus 1160. A description of anexemplary set of specifications for the AHB bus 1160 are set forth in,for example, the AMBA Specification, Revision 2.0 available from ARM,Inc. (www.arm.com).

[0069] During operation of the dual-mode wireless terminal basebandplatform 1100, the Layer 2 processor 1108 executes variousWCDMA-specific functions (e.g., MAC, RLC, PDCP, BMC and RRC), GSM/GPRSstack functions, as well as various common stack functions. InWCDMA-based configurations such as FIG. 11, these common stack functionswould include NAS functions. Finally, the WCDMA baseband co-processor1104 is responsible for all WCDMA-related “Layer 1” or physical layerfunctions.

[0070] In the embodiment of FIG. 11, the host GSM/GPRS basebandprocessor 1101 acts as a master device with respect to the WCDMAbaseband co-processor 1104. The host GSM/GPRS processor 1101 runs aprotocol stack interface that reads and writes to the baseband interface1122 as well as to various registers of the WCDMA baseband co-processor1104. During operation of the platform 1100, the shared memory spacecomprising the baseband interface 1122 facilitates the exchange of databetween the host baseband processor 1101 and the WCDMA basebandco-processor 1104 at regular intervals. When the host baseband processor1101 reads new information stored within this shared memory space, italso writes new information for reading by the WCDMA basebandco-processor 1104. In the exemplary embodiment the host basebandprocessor 1101 may interrupt the WCDMA baseband co-processor 1104 at anytime should it desire to write new data into the shared memory space ofthe baseband interface 1122. This interaction between the host GSM/GPRSbaseband processor 1101 and the WCDMA baseband co-processor 1104facilitates operation of the platform 1100 within a dual-mode system.

[0071] During operation of the dual-mode wireless terminal basebandplatform 1100, both the GSM master timer 1112 and the WCDMA master timer1118 update various counters consistent with the GSM and WCDMAprotocols, respectively. These counters are relevant to control of, forexample, processing of the respective incoming (Rx) and outgoing (Tx)data streams processed by the GSM/GPRS modem 1110 and the WCDMA modem1116.

[0072] Turning now to FIG. 12, an illustrative representation isprovided of a counter 1200 maintained by the WCDMA master timer 1118 ofthe WCDMA baseband co-processor 1104. The counter 1200 includes twofields; namely, a sample counter 1204 and slot counter 1208. In theexemplary embodiment both of the counters 1204 and 1208 are free-runningat every rising edge of the 15.36 MHz system clock (not shown) of theWCDMA baseband co-processor 1104. The sample counter 1204 is incrementedat the 15.36 MHz clock rate and rolls over to 0 upon reaching a count of10239. The slot counter 1208 increments (when its count is less than 14)or rolls over (when its count is equal to 14) when the sample counter1204 rolls over from 10239 to 0.

[0073] As is known to those skilled in the art, the structure ofcounters will vary among communication systems adhering to differentprotocols. For example, the structure of counters maintained by the hostGSM/GPRS baseband processor 1101 differs from that depicted in FIG. 12.

[0074] During operation of the platform 1100, the host GSM/GPRS basebandprocessor 1101 is disposed to synchronize its counters to the countersmaintained by the WCDMA baseband co-processor 1104. In general, the hostGSM/GPRS baseband processor 1101 initiates this synchronization processby either directly or indirectly determining the values of the countersmaintained by the WCDMA master timer 1118. Once the values of thecounters maintained by the WCDMA master timer 1118 have been captured,the host GSM baseband processor 1101 compares the values of the WCDMAcounter values to those maintained by the GSM master timer 1112 anddetermines the timing relationship between the processors 1101, 1104.The determination of this timing relationship effectively synchronizes,within the wireless device incorporating the dual-mode wireless terminalbaseband platform 1100, the timing of the applicable WCDMA and GSM/GPRSnetworks. Establishing such timing synchronization permits the wirelessdevice incorporating the dual-mode wireless terminal baseband platform1100 to operate contemporaneously in WCDMA and GSM/GPRS networks, and/orto be “handed off” between such networks.

[0075] There exist at least two potential methods for synchronizing ordetermining the relationship between the GSM/GPRS and WCDMA counters.Specifically, the host GSM/GPRS baseband processor 1101 may determinethe values of the counters maintained by the WCDMA master timer 1118through execution of either a “direct access read” or an “interruptcapture” method. These methods are described with reference to FIGS. 13and 14, respectively.

[0076] Referring now to FIG. 13, there is shown a timing diagram 1300which illustratively represents a timing synchronization methodpredicated upon execution of a direct access read operation. Pursuant tothis synchronization method, the GSM/GPRS baseband processor 1101performs a direct access read operation upon the “live” counter valuesgenerated by the WCDMA master timer 1118. Consistent with this directaccess approach, the fields of a given counter value generated by theWCDMA master timer 1118 are each read 1150 (FIG. 11) by the GSM/GPRSbaseband processor 1101 during a different deterministic WCDMA clockcycle. In this regard the term “deterministic” indicates that theinstantaneous value of at least one counter maintained by the GSM mastertimer 1112 is known at the time of executing this direct access readoperation; that is, the GSM/GPRS baseband processor 1101 will generallybe configured to perform this direct access read operation when aparticular GSM counter reaches a predetermined value. In FIG. 13, bselis representative of a re-synchronized read pulse received from theGSM/GPRS baseband processor 1101. In addition, baddr represents anaddress bus capable of addressing registers of the WCDMA master timer1118, and brdata corresponds to the data bus through which a register ofthe WCDMA master timer 1118 is read in connection with read operation1150.

[0077] Attention is now directed to FIG. 14, which depicts a timingdiagram 1400 illustratively representing a timing synchronization methodpredicated upon execution of an interrupt capture operation. Asmentioned above, the direct access approach illustrated by FIG. 13generally requires that each field of a given counter value maintainedby the WCDMA master timer 1118 be read during a different deterministicWCDMA clock cycle. In the approach of FIG. 14, all fields of a WCDMAcounter may be captured during the same deterministic clock cycle (i.e.,during the WCDMA clock cycle which occurs upon a given countermaintained by the GSM master timer 1112 reaching a predetermined value).In particular, when a particular GSM counter reaches a predeterminedvalue the GSM/GPRS baseband processor 1101 sends an interrupt pulse 1410to a resynchronization pulse generator 1420 (FIG. 11) of the WCDMAbaseband processor 1104. In response, the resynchronization pulsegenerator 1420 generates a resynchronization pulse 1430 which isprovided to the WCDMA master timer 1118. Upon receipt of this interruptpulse by the WCDMA master timer 1118, the WCDMA modem 1116 is instructedto capture a value 1440 of its sample counter 1204 and a value 1450 ofits slot counter 1208 and store them within its sample_cnt_cap andslot_cnt_cap registers, respectively. This advantageously permits theGSM/GPRS baseband processor 1001 to access these stored values pursuantto a direct access read operation.

[0078] The foregoing description, for purposes of explanation, usedspecific nomenclature to provide a thorough understanding of theinvention. However, it will be apparent to one skilled in the art thatthe specific details are not required in order to practice theinvention. In other instances, well-known circuits and devices are shownin block diagram form in order to avoid unnecessary distraction from theunderlying invention. Thus, the foregoing descriptions of specificembodiments of the present invention are presented for purposes ofillustration and description. They are not intended to be exhaustive orto limit the invention to the precise forms disclosed; obviously manymodifications and variations are possible in view of the aboveteachings. The embodiments were chosen and described in order to bestexplain the principles of the invention and its practical applications,to thereby enable others skilled in the art to best utilize theinvention and various embodiments with various modifications as aresuited to the particular use contemplated. It is intended that thefollowing Claims and their equivalents define the scope of theinvention.

What is claimed is:
 1. A multi-mode wireless communication device,comprising: a first baseband co-processor configured to executelow-level stack operations of a first wireless communications protocolemployed within a first wireless communications network; a host basebandprocessor configured to execute a set of protocol stack operations of asecond wireless communications protocol employed within a secondwireless communications network and higher-level stack operations ofsaid first wireless communications protocol; and a data communicationchannel between said host baseband processor and said first basebandco-processor capable of carrying data received by said multi-modewireless communication device from said first wireless communicationsnetwork or sent by said multi-mode wireless communication device throughsaid first wireless communications network.
 2. The device of claim 1wherein said set of protocol stack operations comprises a complete setof protocol stack operations of said second wireless communicationsprotocol.
 3. The device of claim 1 further including a second basebandprocessor in communication with said host baseband processor via saiddata communication channel, said second baseband processor beingconfigured to execute low-level stack operations of said second wirelesscommunications protocol.
 4. The device of claim 3 wherein said set ofprotocol stack operations comprises higher-level protocol stackoperations of said second wireless communications protocol.
 5. Thedevice of claim 1 wherein said low-level stack operations includephysical layer functions and bearer-specific stack functions peculiar tosaid first wireless communications protocol.
 6. The device of claim 5wherein said higher-level stack functions include stack functions commonto said first and second wireless communication protocols.
 7. The deviceof claim 1 wherein said host baseband processor is further configured toexecute application-layer functions.
 8. The device of claim 1 whereinsaid first baseband co-processor includes: a first physical layer modulefor implementing physical layer functions, a first bearer-specificmodule for implementing bearer-specific stack functions peculiar to saidfirst wireless communications protocol, and a first buffer incommunication with said first physical layer module and said firstbearer-specific module.
 9. The device of claim 8 wherein said firstbaseband co-processor includes a second buffer in communication withsaid first bearer-specific module and said data communication channel.10. The device of claim 9 wherein said host baseband processor includesa common stack functions module and one or more application modules,said common stack functions module executing functions common to saidfirst and second wireless communications protocols.
 11. The device ofclaim 10 wherein said host baseband processor includes a third buffer incommunication with said stack functions module and said one or moreapplication modules.
 12. The device of claim 1 wherein said firstwireless communications protocol comprises WCDMA and said secondwireless communications protocol comprises GSM.
 13. A method performedin a wireless communication device disposed for communication with firstand second wireless communications networks in accordance with first andsecond wireless communication protocols, respectively, said methodcomprising: executing low-level stack operations of said first wirelesscommunications protocol within a first baseband co-processor; executinga set of protocol stack operations of a second wireless communicationsprotocol and higher-level stack operations of said first wirelesscommunications protocol within a host baseband processor; andestablishing a data communication channel between said host basebandprocessor and said first baseband co-processor capable of carrying datareceived by said wireless communication device from said first wirelesscommunications network or sent by said wireless communication devicethrough said first wireless communications network.
 14. The method ofclaim 13 wherein said executing said set of protocol stack operationscomprise executing a complete set of protocol stack operations of saidsecond wireless communications protocol.
 15. The method of claim 13further including executing low-level stack operations of said secondwireless communications protocol within a second baseband processor incommunication with said host baseband processor via said datacommunication channel.
 16. The method of claim 15 wherein said executingsaid set of protocol stack operations comprises executing higher-levelprotocol stack operations of said second wireless communicationsprotocol.
 17. The method of claim 13 wherein said executing saidlow-level stack operations comprises executing physical layer functionsand bearer-specific stack functions peculiar to said first wirelesscommunications protocol.
 18. The method of claim 17 wherein saidexecuting higher-level stack functions includes executing stackfunctions common to said first and second wireless communicationprotocols.
 19. A multi-mode wireless communication device, comprising: afirst bearer-specific processor configured to execute low-level stackoperations of a first wireless communications protocol employed within afirst wireless communications network; a second bearer-specificprocessor configured to execute low-level stack operations of a secondwireless communications protocol employed within a second wirelesscommunications network; a primary processor configured to executehigher-level stack operations common to said first and second wirelesscommunications protocols; a radio transceiver; and means forcommunicating data between said radio transceiver, said primaryprocessor, said first bearer-specific processor and said secondbearer-specific processor.
 20. The device of claim 19 wherein saidlow-level stack operations of said first wireless communicationsprotocol include physical layer functions and bearer-specific stackfunctions peculiar to said first wireless communications protocol. 21.The device of claim 20 wherein said low-level stack operations of saidsecond wireless communications protocol include physical layer functionsand bearer-specific stack functions peculiar to said second wirelesscommunications protocol.
 22. The device of claim 19 wherein said primaryprocessor is further configured to execute application-layer functions.23. A multi-mode wireless communication device, comprising: a firstintegrated circuit configured to execute low-level stack operations of afirst wireless communications protocol employed within a first wirelesscommunications network; a second integrated circuit configured toexecute low-level stack operations of a second wireless communicationsprotocol employed within a second wireless communications network; athird integrated circuit configured to execute higher-level stackoperations of said first wireless communications protocol and of saidsecond wireless communications protocol; a first data communicationschannel between said first integrated circuit and said third integratedcircuit; and a second data communications channel between said secondintegrated circuit and said third integrated circuit.
 24. The device ofclaim 23 wherein said low-level stack operations of said first wirelesscommunications protocol include physical layer functions andbearer-specific stack functions peculiar to said first wirelesscommunications protocol.
 25. The device of claim 24 wherein saidlow-level stack operations of said second wireless communicationsprotocol include physical layer functions and bearer-specific stackfunctions peculiar to said second wireless communications protocol. 26.The device of claim 19 wherein said third integrated circuit is furtherconfigured to execute application-layer functions.